This application claims the priority of Korean Patent Application No. 2004-2665, filed on Jan. 14, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a spindle motor for a disk drive, and more particularly, to a spindle motor for a disk drive having a bearing to support a rotating body in both axial and radial directions in a non-contact manner using aerodynamic pressure.
2. Description of the Related Art
Spindle motors are widely used as a motor for laser beam scanners of laser printers, hard disk drives (HDDs), or optical disk drives using compact discs (CDs) or digital versatile discs (DVDs). The hard disk drive which is one of auxiliary storage devices for computers reproduces information stored on a magnetic disk or records information on the magnetic disk using a magnetic head. The hard disk drives are being developed to keep pace with recent demands for a higher speed, a higher capacity, and a lower vibration. To meet such demands, various researches and developments are under way. In particular, for the high speed and low vibration, studies on a hydrodynamic bearing supporting a rotating body of a spindle motor in a non-contact manner is widely made. Furthermore, studies to adopt a hydrodynamic bearing which reduces a friction force and a starting torque and minimizes a change in the characteristic of a bearing according to a temperature, to hard disk drives for mobile use or an ultrahigh speed use, are made.
In general, a bearing system is composed of a radial bearing to support a load in a radial direction and a thrust bearing to support the load in an axial direction. To reduce vibration of a rotating body a relative position between the radial bearing and the thrust bearing is important. That is, when the radial bearing and the thrust bearing are separated from each other, the relative position between the two bearings needs to be processed to be within a desirable allowance.
FIG. 1 shows a conventional spindle motor adopting a hydrodynamic bearing. Referring to FIG. 1, the spindle motor includes a base 11 and a sleeve 13. A shaft 15 is fixed at a center portion of the base 11. A center hole, in which the shaft 15 is inserted, is formed in the sleeve 13. A coil 12 is provided on the base 11 to generate an electromagnetic force. A magnet 14 corresponding to the coil 12 is provided on the sleeve 13. A bearing gap is formed between an outer circumferential surface of the shaft 15 and an inner circumferential surface of the sleeve 13. The bearing gap is filled with a fluid such as lubricant or grease.
A plurality of grooves 20 are formed on the inner circumferential surface of the sleeve 13 in a herringbone pattern. The grooves 20 generate a hydrodynamic pressure during rotation of the sleeve 13 to support the sleeve 13 in a radial direction of the shaft 15. The grooves 20 are formed in upper and lower portions of the inner circumferential surface of the sleeve 13.
Although not shown in the drawing, a plurality of grooves are formed on the inner circumferential surfaces of the sleeve 13 facing upper and lower surfaces of a flange 25 formed in the upper portion of the shaft 15. These grooves also supports the sleeve 13 in the axial direction of the shaft 15 by generating a hydrodynamic pressure during the rotation of the sleeve 13.
When the spindle motor is adopted to a hard disk drive, the structure of the hard disk drive is complicated due to a sealing design to prevent leakage of the fluid used in the bearing. Also, a power consumption and a starting torque increase due to a friction loss by a viscous frictional force. Further, since the viscosity of the fluid used in the hydrodynamic bearing is considerably changed by heat, the characteristic of the bearing changes greatly according to the heat, which makes the characteristic of the hard disk drive unstable with respect to the heat. Actually, the temperature inside the hard disk drive rises from a room temperature up to 80° C. by the heat generated during operation of the hard disk drive. In contrast, at a low temperature, since the viscosity of the fluid increases, a starting torque needed for the motor is not generated so that the motor may not start.
The spindle motor uses a radial bearing and a thrust bearing to support loads in a radial direction and an axial direction, respectively. In this case, for a highly accurate rotation, the relative position between the radial bearing and the thrust bearing need to be accurately set. However, such setting requires a lots of time for processing and assembly so that productivity is lowered.
A bearing structure to solve the above problem is shown in FIG. 2. FIG. 3 is an exploded view of the bearing structure of FIG. 2. FIGS. 4A through 4C are view to explain an assembly process of the bearing structure of FIG. 2.
Referring to FIG. 2, a bearing structure includes a rotation shaft 30 having upper and lower conic shafts 30a and 30b and sleeves 32a and 32b encompassing a side surface and a lower surface of the rotation shaft 30. The diameter of a section of the rotation shaft 30 increases from the middle portion of the rotation shaft 30 in the lengthwise direction to the opposite ends thereof. The bearing structure having the above structure has a merit of simultaneously supporting the loads in the radial and axial directions. However, to assembly the above bearing structure, as shown in FIG. 3, a sleeve 32 needs to be processed to be at least two parts 32a and 32b and the rotation shaft 30 needs to be at least two parts 30a and 30b. In the assembly process, as shown in FIGS. 4A through 4C, since at least three steps are needed for the assembly process, process and assembly of the bearing structure has problems.